driver provides support for a
to be divided up into a set of pseudo devices called
A Partition can have both a
In general the interfaces are similar to those described by
device has a fairly low level interface to the system,
devices have a much higher level interface and talk to the system via
A scsi adapter must also be separatly configured into the system
before a scsi disk can be configured.
As the scsi adapter is probed during boot, the
bus is scanned for devices. Any devices found which answer as 'Direct'
type devices will be 'attached' to the
driver. The first found will be attached as
driver allows the disk to have two levels of partitioning.
One which allows it to have
partitions for different Operating systems, (one of which is BSD unix),
(see also for the 386 port,
), and within a BSD partition, further partitions which are individually
addressable as separate entries in the
directory. The second level of partitioning is controlled by the program
and is common in format across most BSD operating systems. In most of
the original BSD ports, what is the
BSD part here, is the entire disk, and the outer layer of partitionning
will also run in this manner if
is run with a blank disk, without first partitioning it
Apologies for the two conflicting usages of the word Partition, but
it's a historical artifact, and the meaning must be judged from context
in each case. The next paragraph will discuss partitions exclusively
in the context of WITHIN a BSD partition on the disk.
The first few blocks of the BSD section (maybe all) of the disk contain
some boot code, and a structure, known as the
which describes the disk's characteristics and partitioning for BSD.
program, and read in by the kernel when the device is first initialised
during boot. It describes how the drive is further divided. The
structure contains room for 8 (usually) partitions. Usually these
partitions are calculated so as to fall evenly on cylinder boundaries,
disk this is sometimes not possible. The reason for doing this is historically
to get better performance, however modern
disks often have a variable format, so that it is hard to know at any point
in the disk, where the cylinder or track boundaries are. Added to this, the
disk blocks are addressed soley by their 'block number' and not by
any geometry, leads to the common occurance on
disks, of laying out partitions on arbitrary boundaries. Because
modern disks often have large track caches, this often leads to only small
degadations of performance, and is in fact sometimes unavoidable. The
boot messages will suggest a geometry similar in heads and cylinders
to the real geometry, but the disklable need not agree with this for the
system to be able to successfully work with the disk.
with an uninitialised disk, the
driver will initialise the 'in-core' copy of the disklabel to the suggested
values, however they are not written to the disk.
The fourth partition is special. No matter what the disklabel
says, the fourth partition (partition d) reflectls the entire disk, including
those areas OUTSIDE the BSD partitions. At some times it is suggested that
the c partition might be used to represent the entire BSD partition, so these
two partitions should be avoided when laying out filesystems.
While partitions are only theoretically valid within the BSD partition, they
are specified in terms of absolute block numbers, so it is possible to
specify a partition that lies outside of the BSD partition. This is useful
if one wants to have a /dev entry that points to a partition belonging
to another OS (e.g. DOS).
In configuring, if an optional
the specification, that number of scsi disks are configured;
Most storage for them is allocated only when found so a large number
of configured devices is cheap. (once the first has included the driver).
calls apply to scsi disks as well as to other disks. They are defined
.Bl -tag -width DIOCSDINFO
Usually used to set up a bad-block mapping system on the disk. Scsi
drive incorporate their own bad-block mapping so this is not implimented,
however it MAY be implimented in the future as a 'kludged' interface to the
Read, from the kernel, the in-core copy of the disklabel for the
drive. This may be a ficticious disklabel if the drive has never
been initialised, in which case it will contain information read
from the scsi inquiry commands, and should be the same as
the information printed at boot.
Give the driver a new disklabel to use. The driver will NOT try write the new
Enable or Disable the driver's software
write protect of the disklabel on the disk.
Give the driver a new disklabel to use. The driver WILL try write the new
.Bl -tag -width /dev/rsd[0-9][a-h] -compact
.It Pa /dev/rsd[0-9][a-h]
driver appeared in MACH 2.5 .
projects / unix-history / blob